This disclosure is intended to teach by way of example and not by way of limitation.
This disclosure relates to the field of specialty chemicals. In particular, this disclosure relates to the preparation of salts of 5-sulfoisophthalic acid. More particularly, this disclosure relates to the preparation of various metal (Mt) salts of 5-sulfoisophthalic acid (MtSIPA) from 5-sulfoisophthalic acid (SIPA or HSIPA) via an acetic acid or water or acetic acid/water solvent system using a metal cation producing compound.
Salts of HSIPA, particularly lithium (Li+) and sodium (Na+), are primarily used as additives in the production of polymers. Other salts of HSIPA, or derivatives thereof, are used in a variety of other applications. For example, the silver salt of dimethyl 5-sulfoisophthalate (AgDMSIPA), is used as an antimicrobial additive in polymers. Given that silver is a known antimicrobial agent, it is anticipated that a silver (I) salt of HSIPA will exhibit antimicrobial properties and may also function as a desired additive for certain polymer processes.
Furthermore, it is known in the industry that metal salts of HSIPA (e.g., sodium and lithium) often can be used as substitutes for the same salts of the dimethyl ester of 5-sulfoisophthalate (DMSIPA). The advantages of using 5-sulfoisophthalic acid salts rather than the dimethyl ester salts of 5-sulfoisophthalate include (1) lower cost due to the elimination of a process step (esterification of HSIPA), (2) elimination of the need to vigorously dry the process intermediate (HSIPA) as required during the esterification step of the DMHSIPA process, and (3) elimination of a flammable by-product (methanol) during the preparation of the MtDMSIPA. Thus there is interest in and a need for developing new salts of 5-sulfoisophthalic acid and for exploring their chemical behaviors and potential uses.
Developing a commercially viable method of manufacture for MtSIPA presents several challenges, one of which is the variability in HSIPA chemistry. HSIPA chemistry is such that one cannot necessarily take a known process for making one salt (e.g., LiSIPA), switch out the metal (e.g., switch to Na), and expect that the process will result in a similar salt product. For example, one can wash a crude NaSIPA product with water but doing the same with LiSIPA results in lost product. Likewise, washing crude LiSIPA with acetic acid results in a hydrate or anhydrous product whereas washing crude NaSIPA with acetic acid results in a solvate. Also, one metal cation may require a different solvent system than another metal cation.
In addition, many of the known processes for producing HSIPA salts results in product having high sulfate levels. A high sulfate HSIPA salt can cause problems in polymer processes. For example, LiSIPA salts with accompanying high levels of sulfate are associated with high levels of nylon filament breakage due to sulfate precipitation. Accordingly, HSIPA salts with a low-sulfate composition are of value because they are expected to cause fewer problems in polymer production processes.
For these and other reasons, there is a need for new HSIPA salts and for a manufacturing process that is commercially feasible, economically efficient and avoids or eliminates some of the major problems that hinder other HSIPA salt production methods (e.g., high sulfate levels).